Products packaged in plastic materials but also the packaging materials of plastic themselves are exposed to contact with oxygen in the air, whereby the packaged products but also the packagings are broken down, spoil or detrimentally change in some other way. In the case of foodstuffs there is at best only discoloration due to oxidation reactions, but frequently also there is a faster loss of taste, breakdown of nutritionally relevant substances and growth of micro-organisms and thus the occurrence of substances which are damaging to health such as mould fungi and toxins. Packaged drugs can lose their effect under the influence of oxygen due to oxidative breakdown more quickly than desired and also can lose their original form of administration by virtue of decay reactions. Packaging materials themselves can change in colour or become cloudy or porous under the influence of oxidative breakdown or decay reactions and can lose their sealing integrity so that the packaged products lose their protection due to the packaging material and are exposed to the environmental influences.
Known measures for protecting products or packagings from attack by oxygen in the air include for example the use of composite films as packaging materials, oxygen-resistant coatings on the packaging material, packaging products in a protective gas such as nitrogen and/or carbon dioxide, using antimicrobial substances and preserving substances for preventing the growth of micro-organisms, and the use of oxygen consuming materials as packaging materials.
Oxygen-consuming packaging materials are known in the state of the art. The principle is based on the fact that the packaging material contains an oxidisable substance with which the oxygen in the air can react without the material itself being damaged thereby and the bound oxygen in the air can also no longer react with the packaged products. For example the use of reduced iron powder as an oxygen-consuming material which is embedded in a plastic packaging material is known. The iron reacts with oxygen, with the formation of oxides. An overview of the state of the art in that field is to be found in WO-A-9640412 which itself discloses an oxygen-consuming composition with an oxidisable metal component, an electrolyte component and a non-electrolytic acid component. The acid component serves for activation of the metal in a redox reaction, with formation of metal cations and hydrogen gas from the acid protons. The metal cations can then bind free oxygen, with oxide formation.
One disadvantage and problem with the known oxygen-consuming systems with metal and activating acid is that reaction of the activation of the metal frequently occurs at a very early moment in time, for example already occurring in production of the plastic material or upon transport or storage thereof, before it is used at all for packaging foodstuffs or other products, where the oxygen-consuming effect is first required. A further disadvantage of known systems is that the oxygen-consuming effect is used up early and does not persist for sufficiently long.